A £4,687.80 bill arrives as £7,031.70 on the first 31 January. The extra half is next year, paid early
Payments on Account Calculator
Bills over £1,000 add two payments on account. This is the timeline in dates and pounds, so the first January is a line item instead of a shock.
Payments on Account Calculator
The first Self Assessment January is one and a half bills, not one. This is the timeline, in pounds and dates.
How the system actually works
Bills over £1,000 trigger payments on account: two advance payments of half the bill each, due 31 January and 31 July, unless at least 80 per cent of your tax is already collected at source.
The first January stacks: the whole first bill plus half of it again toward next year. The demo bill of £4,687.80 becomes £7,031.70 due at once, which is the cash-flow shock this tool exists to remove.
If profits fall, you can claim to reduce the payments on account, but reduce too far and HMRC charges interest on the shortfall. Reserve as you earn and January is arithmetic, not drama.
Take the workbook
The two-year payment timeline in Excel with every date and amount.
Download the workbookFAQs
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